Generally, an internal combustion engine receives fuel and air into a combustion chamber and generates power by combusting the fuel and the air. An intake valve is operated by a camshaft, and air flows into the combustion chamber while the intake valve is open. In addition, an exhaust valve is operated a camshaft, and air is exhausted from the combustion chamber while the exhaust valve is open.
Optimal operation of the intake valve/exhaust valve, however, depends on the RPM of the engine. That is, an appropriate time for lifting or opening/closing the valves depends on the RPM of the engine. In order to implement an appropriate valve operation in accordance with the RPM of the engine, as described above, a VVL (Variable Valve Lift) apparatus that operates valves at different lifts in accordance with the RPM of an engine has been studied and employed.
Meanwhile, in a variable valve lift apparatus having a cam shift type which is configured that a plurality of cams are designed for driving a valve and the plurality of cams is moved along an axial direction, it is important that relative position between the plurality of cams and a valve opening/closing unit is exactly controlled.
In a case that relative position between the plurality of cams and a valve opening/closing unit is not exactly controlled, interference may occur between elements for guiding axial direction motion of the plurality of cams and the valve opening/closing unit or between the plurality of cams and the valve opening/closing unit. Thus, the valve opening/closing unit or the variable valve lift apparatus may be damaged, or reliability of a cam shift may be deteriorated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.